IntroductionSeagrass sediments are important ‘blue carbon’ reservoirs which store climatically significant quantities of organic carbon (Corg) at the global scale. Seagrass meadows that overly these sediments also provide a range of critical ecosystem services including shoreline stabilization, storm surge protection, and fisheries nursery grounds. However, the controls over accumulation and the sources of organic C to these sediments beds are highly variable and poorly understood with the relative importance of hydrodynamic setting, species composition and canopy density being unclear.MethodsHere we address these questions using the first observation-based estimates of Corg stocks and provenance on Turneffe Atoll, Belize, made via remotely-sensed habitat extent, local Corg data and isotopic data. Sedimentary Corg was highest in sediments underlying the most sheltered meadows and decreased with increasing exposure to wind and wave energy with the seagrass meadows in the central lagoon containing an extensive deposit of mangrove derived organic carbon, stabilized and protected by the overlying seagrass meadow.ResultsThe influence of species composition appeared weak with the ubiquitous species T. testudinum occurring across a wide range of hydrodynamic regimes ranging from the most sheltered to the most energetic and being associated with a wide range of sedimentary organic C concentrations. Importantly from the perspective of remote sensing, org C concentrations were unrelated to canopy density. We hypothesize that this decoupling of organic C concentration from seagrass canopy cover reflects a much longer timescale for carbon storage in the sediments than the lifespan of the seagrass plants themselves and/or a substantial non seagrass derived organic C burden in seagrass sediments. Overall, we conservatively estimate that the top 30cm of sediments underlying the seagrass meadows overlying carbonate sediments on the atoll exterior store 0.58 x 106 Mg Corg, most of which is seagrass-derived, whilst the sediments underlying the meadows within the central lagoon store an additional 1.28 x 106 Mg Corg. When the maximum possible extent of seagrass is considered, this estimate increases to 3.54 x 106 Mg Corg. Substantial Corg stocks extending >1m depth were observed across all sites, and so these inventories are considered conservative.DiscussionA preliminary ‘cost of loss’ for sedimentary Corg in the top 30 cm of Turneffe Atoll’s seagrass meadows, based on a carbon trading value of €60 tCO2 (eq), is estimated at €42 million for the outer atoll, increasing to €136 million when the mangrove-derived sediments of the central atoll are considered and €260 million when turbid areas are assumed to contain seagrass.

中文翻译：

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量化与伯利兹 Turneffe 环礁海草草甸树冠覆盖率相关的沉积“蓝碳”


简介海草沉积物是重要的“蓝碳”储层，在全球范围内储存了大量的有机碳 （Corg）。覆盖这些沉积物的海草草甸还提供了一系列关键的生态系统服务，包括海岸线稳定、风暴潮保护和渔业苗圃。然而，这些沉积物床对积累和有机碳来源的控制变化很大，并且由于水动力设置、物种组成和冠层密度的相对重要性尚不清楚，人们知之甚少。方法在这里，我们使用通过遥感栖息地范围、当地 Corg 数据和同位素数据对伯利兹 Turneffe 环礁的 Corg 种群和来源的首次基于观测的估计来解决这些问题。沉积性 Corg 在最隐蔽的草甸下方的沉积物中最高，并且随着暴露于风能和波浪能的增加而减少，中央泻湖中的海草草甸包含大量红树林衍生的有机碳沉积物，由上覆的海草草甸稳定和保护。结果物种组成的影响似乎较弱，无处不在的物种 T. testudinum 出现在从最隐蔽到最有活力的广泛水动力状态中，并与广泛的沉积有机 C 浓度有关。重要的是，从遥感的角度来看，组织 C 浓度与冠层密度无关。 我们假设有机碳浓度与海草树冠覆盖物的这种脱钩反映了沉积物中碳储存的时间尺度比海草植物本身的寿命和/或海草沉积物中大量的非海草衍生的有机碳负荷要长得多。总体而言，我们保守估计，环礁外部碳酸盐沉积物上覆盖的海草草甸底部 30 厘米的沉积物储存了 0.58 x 106 毫克崎岬，其中大部分是海草衍生的，而中央泻湖内草甸下的沉积物储存了额外的 1.28 x 106 毫克崎崽。当考虑到海草的最大可能范围时，这个估计增加到 3.54 x 106 毫克高谷。在所有地点都观察到大量 Corg 储量延伸 >1m 深度，因此这些库存被认为是保守的。讨论根据 60 吨二氧化碳 （eq） 的碳交易价值，特内夫环礁顶部 30 厘米沉积岩峦的初步“损失成本”估计为外环礁 4200 万欧元，如果考虑到中央环礁的红树林衍生沉积物，则增加到 1.36 亿欧元，如果假设浑浊地区含有海草，则增加到 2.6 亿欧元。